spi: Fix reference count leak in slave_show()

Fix a reference count leak in slave_show() by properly putting the device
reference obtained from device_find_any_child().

Fixes: 6c36406 ("spi: core: Add support for registering SPI slave controllers")
Fixes: c21b083 ("spi: Use device_find_any_child() instead of custom approach")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20250319032305.70340-1-linmq006@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -2954,9 +2954,13 @@ static ssize_t slave_show(struct device *dev, struct device_attribute *attr,
 	struct spi_controller *ctlr = container_of(dev, struct spi_controller,
 						   dev);
 	struct device *child;
+	int ret;
 
 	child = device_find_any_child(&ctlr->dev);
-	return sysfs_emit(buf, "%s\n", child ? to_spi_device(child)->modalias : NULL);
+	ret = sysfs_emit(buf, "%s\n", child ? to_spi_device(child)->modalias : NULL);
+	put_device(child);
+
+	return ret;
 }
 
 static ssize_t slave_store(struct device *dev, struct device_attribute *attr,